Additive manufacturing techniques and processes generally involve the buildup of one or more materials to make a net or near net shape (NNS) object, in contrast to subtractive manufacturing methods. Though “additive manufacturing” is an industry standard term (ASTM F2792), additive manufacturing encompasses various manufacturing and prototyping techniques known under a variety of names, including freeform fabrication, 3D printing, rapid prototyping/tooling, etc. Additive manufacturing techniques are capable of fabricating complex components from a wide variety of materials. Generally, a freestanding object can be fabricated from a computer-aided design (CAD) model.
A particular type of additive manufacturing, or 3D printing, technique and process generally includes forming and extruding a bead of flowable material (e.g., molten thermoplastic), applying such bead of material in a strata of layers to form a facsimile of an article, and machining such facsimile to produce an end product. Such a process is generally achieved by means of an extruder mounted on a computer numeric controlled (CNC) machine with controlled motion along at least the X, Y, and Z-axes. In some cases, the flowable material, such as, e.g., molten thermoplastic material, may be infused with a reinforcing material (e.g., strands of fiber) to enhance the material's strength. The flowable material, while generally hot and pliable, may be deposited upon a substrate (e.g., a mold), pressed down or otherwise flattened to some extent, and leveled to a consistent thickness, preferably by means of a tangentially compensated roller mechanism. The flattening process may aid in fusing a new layer of the flowable material to the previously deposited layer of the flowable material. In some instances, an oscillating plate may be used to flatten the bead of flowable material to a desired thickness, thus effecting fusion to the previously deposited layer of flowable material. The deposition process may be repeated so that each successive layer of flowable material is deposited upon an existing layer to build up and manufacture a desired component structure. When executed properly, the new layer of flowable material may be deposited at a temperature sufficient enough to allow new layer of flowable material to melt and fuse with a previously deposited layer of flowable material, thus producing a solid part.
While the aforementioned process achieves a near net shape much faster than depositing down a large number of very thin layers, a surface milling or other finishing operation is required to achieve the final net shape of the article, since it is deposited in stepped layers of tamped, extruded material. Such milling or finishing generally is accomplished using a rapidly spinning cutting tool with a round shaped tip, requiring numerous passes over the surface of the article, shifting over a small distance after each pass to generate the desired surface finish. In order to achieve a smooth surface, the amount the tool path is shifted after each pass must be relatively small; necessitating a large number of passes, which in turn requires considerable time to complete. While this approach may be satisfactory for a single item or a prototype part, it is less desirable for the production of multiple identical parts.
In view of the foregoing, the present disclosure provides systems and methods for producing articles from thermoplastic or flowable material using additive manufacturing techniques, which can generate multiple articles that are dimensionally accurate, and replicate the desired shape and surface features in less time, less effort, and reduced cost. Consequently, the present disclosure provides aspects of methods and apparatus for producing dimensionally accurate articles, which embody surface properties of sufficient quality, so as to negate the need for finishing operations.